This invention relates to additives for oleaginous fluids containing extreme pressure and antiwear agents and containing less than 15 wt. % higher dialkyl polysulfides and to a method for their manufacture.
Methods for preparing dihydrocarbyl polysulfides, such as dialkyl polysulfides based on the use of mercaptans and sulfur as raw materials are well known in the art and are described for example in U.S. Pat. Nos. 2,237,625, 3,022,351, 3,275,693, 3,308,166, 3,314,999, 3,340,321, 3,392,201, 3,452,100, 3,755,461, 3,994,979, 4,564,709, 4,876,389, 4,933,481, and 4,937,385; British Pat. Spec. No. 1,160,473; Canadian Pat. Nos. 839,767 and 885,990; European Pat. App. Pub. No. 25,944 and 337,837; and Japan Kokai (Laid-Open application) Nos. 58-140,063.
Another approach for producing dihydrocarbyl polysulfides involves oxidizing a mercaptan with air or free oxygen in the presence of a catalyst. In U.S. Pat. No. 2,558,221, the catalyst is a selected natural bauxite which contains on a weight basis 50-70% Al.sub.2 O.sub.3, 8-20% Fe.sub.2 O.sub.3, 2-8% SiO.sub.2, 0.5-5% TiO.sub.2, and 2-30% volatile matter as determined by ignition at 1800.degree. F. In U.S. Pat. No. 2,574,884 the catalyst is alumina associated with a minor amount of vanadia, magnetic iron oxide or chromia. In U.S. Pat. No. 4,277,623 a catalyst system comprising a cobalt molybdate-alkali metal and/or alkaline earth metal hydroxide is used as the oxidation catalyst. And in U.S. Pat. No. 4,288,627 the oxidation catalyst is a supported cobalt molybdate catalyst used in combination with a liquid tertiary amine.
It is also known that dihydrocarbyl polysulfides can be formed by reacting mercaptans with sulfur chlorides such as sulfur monochloride and sulfur dichloride.
Of the various dihydrocarbyl polysulfides, dihydrocarbyl trisulfides are particularly desirable for use as extreme pressure lubricant additives because of their superior performance capabilities and their generally lower corrosiveness towards "yellow metals" such as copper. Higher hydrocarbyl polysulfides (e.g. polysulfides with more than about 3 sulfur atoms per molecule) are less desirable than polysulfides containing 3 or less sulfur atoms per molecule. Hence, one object of this invention is to provide a process which yields additives containing a high percentage of dihydrocarbyl di- and trisulfides and less higher dihydrocarbyl polysulfides.
Combinations of sulfur containing organic compounds and organo phosphorus compounds are described for example, in U.S. Pat. No. 3,583,915, wherein di(organo)phosphonates having the following structure ##STR1## wherein R.sub.1 and R.sub.2 are individually alkyl or alkenyl groups having from 1 to 30 carbon atoms and at least one of which is an aliphatic group of at least 14 carbon atoms, are admixed with an active sulfur compound. Active sulfur compounds include organic sulfides and sulfurized hydrocarbons having up to 65% sulfur.
U.S. Pat. No. 3,510,426 describes lubricant compositions containing an alkyl phosphite and at least one sulfurized olefin selected from the group consisting of sulfurized butylenes and sulfurized cyclopentadiene. The lubricant compositions of this invention are said to have desirable extreme pressure properties.
U.S. Pat. No. 4,744,912 describes methods for the preparation of reaction products of sulfurized olefins, dialkyl hydrogen phosphites and primary alkyl amines as well as lubricant compositions containing same. Sulfurized olefins may be prepared, for example in accordance with U.S. Pat. Nos. 3,703,504 or 3,703,505. The dialkyl hydrogen phosphites have the general formula ##STR2## where each R is independently C.sub.1 to about C.sub.30 alkyl. The amines have the general formula EQU R.sub.3 NH.sub.2
wherein R.sub.3 may be alkyl, aryl, alkaryl, aralkyl, cycloalkyl or substituted moieties thereof having from about 1 to about 30 carbon atoms, when aryl it contains from 6 to about 14 carbon atoms in the aryl group.
Japan Kokai 59-10559 describes a process wherein dialkyl polysulfide is treated with an aqueous solution of sodium sulfide or phosphine compound at 30.degree.-80.degree. C. for 1-5 hours. The dialkyl polysulfide type material is produced by reacting alkylmercaptan with sulfur to form a dialkyl trisulfide type material which is then treated to improve the copper corrosion properties. The treated product is indicated to have reduced copper corrosiveness; and the applicants, in that laid open application, express their belief that the reduction in copper corrosiveness is due to a chemical reaction whereby diakyl tetrasulfide and dialkyl pentasulfide are converted into a less corrosive diakyl trisulfide and sodium polysulfide, or triphenylphosphine sulfide and trilauryltrithiophosphine sulfide etc.
U.S. Pat. No. 4,900,460 relates to reaction products of dihydrocarbyl phosphates and phosphites and a particular sulfurized olefin and to lubricant compositions containing same. The sulfurized olefins are characterized as having no remaining olefinic bonds. The dihydrocarbyl phosphates and phosphites are reacted, in accordance with this invention, with sulfurized olefins in the absence of any added catalyst.